IR Digital Holography Lets Firefighters See Through Flames

ROME, Feb. 26, 2013 — Finding a person hidden in a blazing, smoky fire should become a little easier for firefighters, thanks to a new lensless infrared digital holographic imaging technology that can “see” flames.

Firefighters can see through smoke using the current IR camera technology, but seeing through the flames themselves is problematic, because the intense IR radiation that they emit often overwhelms the sensitive detectors, rendering them less effective than they could be.

By employing a specialized lens-free technique, researchers at the Consiglio Nazionale delle Ricerche (CNR) have developed a system that can cope with the flood of radiation from an environment filled with flames and smoke.

To see through smoke, scientists employ lenses to collect and focus light, but using the same technique with flames results in saturation in some areas of the resulting image (top). The new CNR system does not employ a lens, so collected light is distributed over the whole array of camera pixels, avoiding this saturation and the blind spots it produces (bottom). Images courtesy of Optics Express.
“IR cameras cannot 'see' objects or humans behind flames because of the need for a zoom lens that concentrates the rays on the sensor to form the image,” said Pietro Ferraro of CNR’s Istituto Nazionale di Ottica. By eliminating the need for the zoom lens, the new technique avoids this drawback.

“It became clear to us that we had in our hands a technology that could be exploited by emergency responders and firefighters at a fire scene to see through smoke without being blinded by flames, a limitation of existing technology,” Ferraro said. “Perhaps most importantly, we demonstrated for the first time that a holographic recording of a live person can be achieved even while the body is moving.”

Unlike visible light, beams of IR light scattered in a room can penetrate thick smoke and flames without obstruction. IR light, however, reflects off objects, such as the contents of a room or people in danger, and the information carried by this reflected light is recorded by a holographic imager. It is then decoded to reveal objects beyond the smoke and flames, resulting in a live 3-D movie of the room and its contents.

Two images of a human subject as seen through flames. When viewed in infrared or white light, the man is almost completely occluded (left). The new system reproduces the image behind the flames using holography, revealing a man wearing a T-shirt and glasses (right).
To make this technology portable, the investigators will develop a tripod-based system that houses both the laser source and the IR camera. The system could also serve as a fixed installation inside buildings or tunnels.

The team is now exploring other applications, most notably in the biomedical field.

“Besides life-saving applications in fire and rescue, the potential to record dynamic scenes of a human body could have a variety of other biomedical uses including studying or monitoring breathing, cardiac beat detection and analysis, or measurement of body deformation due to various stresses during exercise,” Ferraro said. “We are excited to further develop this technology and realize its application for saving and improving human life.”